In structural dynamics, modal analysis permits normal mode representation
for vibrating structures by recording multiple transfer functions and letting a
computer animate a simple harmonic oscillator approximation to display normal
mode motion in an expanded time frame. This work shows an example of applying
this technique to the representation of a sound field. Phase information is
recorded by using the excitation source as a reference signal, monitoring the
sound field with a microphone, and forming a transfer function of the two with
a dual channel FFT analyzer. The method is illustrated by showing the sound
field above and below the sound board of a grand piano, and in a vertical plane
in the general direction of an audience.